Quality control in livestock feed plant

Pashu Sandesh, 28th June 2017

Dr. T. Susmita

Quality control in livestock feed plant is of utmost importance for overall success and profitability of livestock enterprises. No other factor, directly or indirectly related to proper nutrition and high performance of animals is more critical than feed quality control and ration consistency. The relationship between feed quality and animal performance is important and encompasses not only the quantitative amounts of all feed components but also the digestibility and metabolism of those components.Quality control of incoming ingredients is crucial to predicting the quality of a finished feed. A large number of raw materials are considered for the production of livestock feed, based on their chemical composition and current price structure. The processing techniques, such as oil extraction, polishing etc., are the factors, which affect the composition of raw materials. Adulteration of raw materials is also quite common. Hence, it is essential to observe strict quality control measures for the purchase of raw materials.

1.1 Sampling

Since the samples form the base for analysis, utmost attention should be taken in drawing out samples. It is generally found that the raw materials supplied are not of uniform quality. It is also common to note that some suppliers send the consignments with good quality materials in the periphery of gunny bag and inferior material in the centre. Hence, the sample should be drawn from the centre as well as from the periphery of the gunny bags. It is better to draw samples from all the bags (100 percent sampling) as far as possible. 100 percent sampling proves to be an efficient system for detecting adulteration during the receipt of material. Every consignment should be given a separate code number so that it can be recorded for analysis, reporting and issuing. In India, Bureau of Indian Standards (BIS) has laid down the following procedures and precautions for collecting the samples for analysis:

1.1.1 General requirements of sampling

In drawing, preparing, storing and handling samples, care should be taken that the properties of feeds are not affected.

Take a sample at a protected place not exposed to damp air, dust or soot.

The sampling instrument shall be clean, dry and sterile when used.

Protect the samples, the sampling instrument and containers for samples from adventitious contamination.

Preserve samples in clean, dry and sterile containers. The sample containers shall be of such a size that they are almost completely filled by the sample.

Each container shall be sealed air-tight with a stopper or a suitable closer after filling in such a way that it is not possible to open and reseal it without detection. Market full details of sampling i.e. the date of sampling, batch or code number, the name of the manufacturer and other important particulars of the consignment.

The sample shall be stored in sample storage room (Fig. 1.1) in such a manner that there is no deterioration of the material.

Sampling shall be done by a person agreed to between the purchaser and the vendor and if desired by any of them, in the presence of the purchaser (or his representative) and the vendor (or his representative).

1.1.2 Scale of Sampling

 Quantity of cattle feed of a particular type, produced under relatively similar conditions in a day shall constitute a lot.

Samples shall be tested for each lot for ascertaining conformity of the material to the requirements of the standard.

The number of bags to be selected from the lot shall depend on the size of the lot and shall be in accordance with Table 1.1

1.2 Evaluation of feeds and feed ingredients for quality

The feeds are usually subject to the following types of tests:

1. Physical evaluation

2. Chemical evaluation

1.2.1 Physical evaluation

Physical evaluation is easy but rough in nature. One must be highly trained to identify the changes in the nature of the raw materials/ feeds.

Colour

The appearance of the ingredient will reveal its quality. Any change in the colour of the feed ingredients gives an indication of the maturity of the grain, storage conditions, presence of toxins, contamination due to sand, possible use of insecticides/ fungicides which give dull and dusty appearance. Orange to the red colour of sorghum indicates high tannin content. Browning or blackening due to heat on improper storage reduces nutritive value.

Size

The size of the grains governs its energy value due to the proportional decrease/increase in seed and its coat. Smaller the grain, lower will be the metabolizable energy (ME) value due to more proportion of coater hulls. To evaluate the cereals, the weight of a fixed number of grains usually 100 grains or fixed volume is taken. A Higher weight indicates a higher ME value. This technique is called Test Weight.

Homogeneity

The presence of contaminants like other grains, husk, broken grains, weed seeds, infected seeds is viewed. In the oil seed cakes, closer observation will reveal the presence of fibrous material, especially in de-oiled groundnut cake. Rice polish is contaminated with husk. Clumps in mineral ingredients are not suitable for premixing.

Smell

Smell is the next best indicator. Just standing near the stock itself will immediately indicate any difference in the normal smell. The plant manager should familiarise himself with the normal smell of the ingredients; any change in the normal smell of the ingredients should be viewed with suspicion. Musty odour indicates the beginning of fungal contamination or boring insects. To detect rancidity in oil-rich feed ingredients this is the best method. The odour of petroleum products is suggestive of excessive pesticide or fungicides.

Taste

Each ingredient has a different taste, any change in the taste like bitterness in grains, soya, sunflower oil meal and groundnut cake indicates the presence of mycotoxins. The level of salt can be detected by tasting the ingredient and the feed. The bitter taste of rice polish indicates rancidity of fatty acids.

Touch

Feeling the raw material will indicate dryness. Chilliness indicates high moisture content. Clumps can be detected by inserting a hand into the bag. Clumps may be formed due to high moisture content, improper storage, packing of fresh warm solvent extracted meal, which crumbles on the application of light pressure. Clumps formed due to excess of moisture will be very hard. To evaluate rice polish, place about 25g of rice polish on the palm and close the fingers tightly and then open the fingers, the rice polish will become like a solid mass if the crude fibre level is below 12 per cent. If the fibre level is high, the mass will disintegrate once the fingers are opened. Further pressure will be felt when the hand is closed in high fibre rice polish.

Sound

Dry grains on pouring down or biting will produce the sound of spilling coins.

1.2.1.1 Common adulterants in feeds

Adulteration is defined as the admixture of a pure substance with some cheaper and low-quality substance. It is done intentionally usually to make money. In costly feed ingredients like oil seed cakes, adulteration is done by spraying urea in order to raise their protein content. However, sometimes bran are also added. Besides urea, oilseed cakes are adulterated with husk, non-edible oilseed cakes etc.

The common contaminant or adulterant is husk or sand (Table 1.2). Winnowing is the best method to detect husk in the feedstuffs. Sieving can be done to differentiate contaminants based on particle size.

1.2.1.2 Spot tests for detection of various types of adulteration

Mahua cake

To water extract of the test feed, add concentrated H2SO4 (sulphuric acid). Violet or pink colour indicates the presence of mahua cake.

Argemone seeds

To water extract of test feed, add conc. HNO3 (nitric acid). The appearance of brown-reddish colour indicates the presence of argemone seeds.

Detection of castor cake in feedstuffs

When feed is treated with potassium chlorate, the castor cake is destroyed and settles down at the bottom.

Detection of neem seed cake in feedstuffs and edible oil cakes

The coarsely powdered feed stuff are percolated three times at room temperature with 95 per cent alcohol. The total percolate is concentrated under reduced pressure till a thick syrupy amber coloured residue is obtained, which is treated with different solvents to extract a crystalline product (Nimbine). It is cautiously dissolved in concentrated sulphuric acid, the resultant brown solution changes to cherry red on  the addition of small quantity of concentrated nitric acid. The crystalline product gives a yellow colour with tetranitromethane. An alcoholic solution of the crystalline product shows a sky blue fluorescence under ultraviolet light.

Detection of linseed meal in animal feeds

A small quantity of feed is treated with 1 or 2 drops of dilute sulphuric acid in a test tube. It is sometimes necessary to add some granulated zinc and more acid. The mouth of the test tube is covered with a disk of filter paper moistened with a drop of reagent. Depending upon the amount of hydrogen cyanide produced a more or less intense blue colour appears on the reagent paper. Gentle warming in a water bath is advisable when a small quantity of cyanide is suspected.

1.2.1.3 Urea spot test

Procedure

A) Weigh 2.5 g urease powder with small amount of distilled water, stir into a paste and dilute to 50 ml with distilled water.

B) Rub 0.15 g bromothymol blue indicator powder in a mortar with 2.4 ml 0.1 N NaOH (Sodium Hydroxide) solution. After indicator dissolves, wash mortar and pestle with distilled water and dilute to 50 ml with distilled water. The solution should be green; pH approx. 7.0.

C) Mix solution (A) and (B) in equal proportion.

Take 90 ml mixture solution of (C) and mix with 10 ml glycerol.

Pour mixture into a watch glass. Dip pieces of heavy filter paper in solution. 

Allow drying papers in a place free from NH 3 fumes, strong air currents or heat.

The paper should be orange when dried.

Make strips of these papers and store in an amber coloured glass bottle in a cool place.

Testing

Dissolve a small quantity of feed/ feed ingredients with distilled water in a beaker.

Deep the strip in a beaker and allow to dry it.

The appearance of a blue colour indicates the presence of urea.

1.2.1.4 Identification of plant and animal protein in feed

1. Mix 1-2 g test sample with 100 ml boiling water or boil the mixture for 2-3 min. Place a few ml of the cooled mixture in a test tube and add 5-6 drops of iodine solution. If starch is present, the mixture turns blue.

2. Spread 1-2 g test sample into a petri dish. Add 5-6 drops of iodine solution and let stands for 10 min. A purple-brown colour indicated the presence of plant fibre, whereas yellow indicated animal fibre (protein) using a microscopic examination.

1.2.1.6 Spot tests for toxic constituents

Nitrates

Reagents

Diphenylamine

Concentrated sulphuric acid

Distilled water 

Procedure

Place the material to be tested in a white spot plate. Add 2 to 3 crystals of diphenylamine and a drop of water. Add a drop of concentrated sulphuric acid.

Positive results

The presence of nitrate will produce a deep blue colour.

Cyanogenic glycosides (HCN) in feeds

Procedure

Prepare sodium picrate paper by dipping strips of filter paper into 1% picric acid solution and dry. Again dip it into 10% Na2CO3 solution and dry. Store these papers in a stoppered bottle.

Take a small amount of ground feed sample in a test tube. Insert a piece of moist sodium picrate paper in a tube, taking care that it does not come in contact with the sample. Add few drops of CHCl3 (chloroform) and stopper tube tightly.

Results

If cyanogenic glycosides present in the feed, sodium picrate paper gradually turns orange, then brick red.

Note: Test is delicate and rapidity of change in colour depends upon the amount of free HCN present. This test works well with fresh plant materials but relatively less sensitive to dry substances, particularly ground.

Aflatoxin

Reagents

Methanol

N-hexane

Benzene

Anhydrous sodium sulphate

Green basic cupric carbonate

Procedure

Take 100 g of dry ground sample in a mixer and add 300 ml of a solvent methanol: water (7:3). Mix the content at a higher speed for 5 minutes. Allow to settle and then filter through a double layer of muslin cloth using a vacuum. Take 100 to 150 ml liquid filtrate in a separating funnel. Add 30 ml benzene and shake for one minute and add 200 ml distilled water. Allow to settle and discard lower layer. Place the upper layer into a beaker and evaporate to complete dryness. Re-suspend in 0.5 ml benzene. Spot 50 μl on Whatman filter paper No. 4. Allow the spot to dry and place it under a long wave UV light.

Results

Development of a blue fluorescence colour on it clearly indicates that the sample contains aflatoxins. This method can detect aflatoxins at 10 to 15 ppb.

1.2.1.7 Other tests

Salt (NaCl)

Reagents

Silver nitrate solution (5per cent)•

Nitric acid solution (1:2)•

Ammonium hydroxide solution (1:1)•

Standard sodium chloride solution (0, 0.1, 0.2 and 0.3 per cent)•

Procedure

Weigh 1 g of feed sample and add 100 ml of distilled water. Stir and filter through Whatman filter paper no. 4. Take 1 ml of above feed solution and 8 ml of nitric acid solution in a test tube. Stir and add 1 ml of silver nitrate solution. Similarly add 1 ml standard solution (0, 0.1, 0.2 and 0.3 per cent) in a different test tube and add 1 ml of silver nitrate solution. Compare the test sample with the standard sample. The test should be read within 5 minutes.12

Positive results

The presence of salt will produce a white turbidity.

 Meat cum bone meal and leather meal

Reagents

Ammonium molybdate solution: Dissolve 5 g of ammonium molybdate in 100 ml of distilled water and add into 35 ml concentrated nitric acid.

Procedure

Place few feed particles in a petri dish. Add 3 to 5 drops of ammonium molybdate and let it stand for 5 to 10 minutes.

Positive results

The presence of meat cum bone meal will produce a greenish yellow colour. Leather meal gives no colour change.

Blood

Reagents

Solution A: Dissolve 1 g of N, N-dimethylaniline in 100 ml of acetic acid and 150 ml of distilled water.

Acetic acid

Hydrogen peroxide (3 percent)

Procedure

Place a few particles of feed sample on a slide. Mix 4 parts of solution A with 1 part of 3per cent hydrogen peroxide. Add 1 to 2 drops of this solution on feed sample.13

Positive results

If blood is present, a dark green colour will develop around the feed particles. Low magnification stereo microscope can be used to observe the colour.

Dr. T. SUSMITA,
 Assistant professor,
 Dept of poultry science,
   NTR. CVSc, Gannavaram.